1. Field of the Invention
The invention relates to printing apparatuses such as dot-matrix printers and bit-image printers, and more particularly to printing apparatuses in which the dot printing mechanism utilizes nozzles and wires forming the individual dots positioned in a zigzag formation alternately on multiple strings.
2. Description of the Related Art
Impact-type dot printers and non-impact-type dot printers, such as ink-jet printers, use print heads in which the dot-printing mechanism, which use wires and nozzles to print individual dots and to achieve high resolution, are positioned in a zigzag formation. FIG. 15 illustrates an ordinary circuit from one such printer for sending the printing data that has been expanded into a bit-map image to the print head. Multiple nozzles 8, which print dots in correspondence to the individual bits of the printing data which has been formed into a bit map, are positioned in two strings on printing area 10 of the print head, as shown in FIG. 16. For example, a total of 128 dots can be printed. Of these nozzles, the odd-numbered nozzles are positioned on first line 11, and even-numbered nozzles are positioned along second line 12 which is separated from line 11 by distance l. Since print head 10 prints data by reciprocating over the paper surface either in the transverse or longitudinal direction, positioning nozzles 8 in such a zigzag formation enables high-resolution printing without reducing the space occupied by nozzles 8 and the mechanism required by nozzles 8. In print head 10 illustrated in FIG. 16, although the space between nozzles is 2d, high-resolution printing with a dot pitch of d can be achieved.
In a conventional circuit such as that illustrated in FIG. 15, bit data for all dots (e.g., 128 dots) of line 11 or 12 (i.e., n-th string), whichever is to be printed first depending on the direction of the head movement, is selected from printing data 21 that has been bit-mapped and stored inside image buffer 20. This selected bit data is converted into serial data by parallel-serial conversion circuit 25, and is sent to the print head. However, because the nozzles of print head 10 are positioned in a zigzag formation and nozzle strings 11 and 12 are separated by distance l, the bit data of the n-th string (string n) sent from image buffer 20 cannot be set in nozzle string 11 or 12 as is. Therefore, selection circuit 18 is provided to select the bit data corresponding to odd-numbered dots and the bit data corresponding to even-numbered dots, and the bit data for the nozzle of the line to be printed first (e.g., odd-numbered nozzle string 11) is converted into parallel data by serial-parallel conversion circuit 13, which is then set in nozzle string 11 by latch circuit 15. The bit data for the remaining even-numbered nozzle string 12 is temporarily stored in buffer circuit 19. When even-numbered nozzle string 12 moves to the position for printing the bit data stored in buffer circuit 19, the remaining bit data is set in even-numbered nozzle string 12 via serial-parallel conversion circuit 14 and latch circuit 16, and is then printed.
Consequently, buffer circuit 19 must be equipped with memory that can store the bit-mapped data to be printed at distance l between two nozzle strings 11 and 12 and with a circuit for controlling this memory. Furthermore, to print in both directions in which the print head travels, the connection between buffer circuit 19 and selection circuit 18 must be switched depending on whether nozzle string 11 or 12 is to print first. The connection between buffer circuit 19 and serial-parallel conversion circuit 13 or serial-parallel conversion circuit 14 must also be switched. Otherwise, it is necessary to provide multiple buffers for nozzle strings 11 and 12.